The sign at the entrance of the 303rd Logistics building lists "CSM E.L Haney" as the unit's Command Sergeant Major. Eric L. Haney is the author of Inside Delta Force, the book upon which the show is based.
The T-shirt hanging in Alpha Team's ready room says "Welcome to the US Army" with the acronym "BOHICA" painted underneath. This is a subtle nod to SEAL Team SIX creator Richard Marcinko who coined the term.
The Unit, the cover name for the most elite 1st SFOD-D unit popularly known as "Delta Force", the Army's best of the best, primarily recruits from Army Special Forces Groups ("Green Berets") and the 75th Ranger Regiment (Army Rangers). In The Unit, Jonas Blane, Hector Williams, and Charles Grey all served as both Rangers and Green Berets prior to their service in The Unit. Mack Gerhardt served as a Ranger and in the airborne infantry prior to being in The Unit. Bob Brown is the only Unit member to have never served in the Rangers. He is Ranger qualified (graduated from Ranger School) and served in the Air Cavalry prior to joining the Unit.
In the Image Comics comic book series titled "The Activity" by Nathan Edmondson and Mitch Gerads, The Unit character of Mack Gerhardt is alluded to / paid homage to in issue #12 titled "Higher Ground." In the issue a special operations team, alluded to later in the issue as Delta Force, are making their way toward their mission in Fallujah. One of the team members is referred to by name as "Gerhardt." Later in the issue the team's individual call signs are named, and one of the call signs is "Dirt Diver." "Dirt Diver" is used numerous times as the designated call sign of Master Sergeant Mack Gerhardt in The Unit.
Several members of the Unit may have had an unofficial cameo in the BMW film 'Ticker'. When the Driver arrives at a military base, Robert Patrick and Dennis Haybert are seen playing plain clothes agents, looking much how they look in various episodes when they were protecting high value assets.
The names on the whiteboard on the refrigerator of the team's ready room (where the team indicates the number of beers they owe) are the real names of the cast and crew, not the names of their characters.
The trivia item below may give away important plot points.
The death of beloved Unit member Hector Williams is still a controversial topic amongst fans to date. None of the cast, including actor Demore Barnes who portrayed Hector Williams, were aware that his character would be killed off until they received the script for the episode. The character was a fan favorite, and the writers and producers chose to kill off Williams to retain an air of believability in the storylines that some times the good guys and heroes do get killed in combat. There is also a significant number of fans who at first believed that Williams was killed off in secret on the orders of Colonel Tom Ryan by an unknown assassin, due to Williams accidentally catching Ryan dead to rights in an affair with Tiffy Gerhardt (Mack's wife) at a hotel they coincidentally all wound up staying at off post. It was theorized that Williams was killed off by Ryan to keep the affair secret, though the idea of Ryan killing off Williams was disproven in the series plot later.